Antifuses are used in integrated circuits to provide various circuit selection and configuration functions. When fabricated in a MOS technology, analog components, such as comparators or amplifiers, for example, may require an adjustment of operating parameters. Antifuses are used to select device configurations to effect parameter value adjustments.
The antifuse is blown by applying a higher than normal voltage or laser beam to the antifuse. The high voltage, for example, produces a short circuit where an open circuit once existed. The application of the laser beam creates a similar short circuit condition. The blown antifuse alters a high impedance situation to a current conducting path that effects a change in a logic level with an applied current. The antifuse generally comprises two conductors, either metal and/or a semiconductor material, having some kind of dielectric or insulating material between the two conductors. In recent practice the dielectric is set to approximately half the normal thickness of a thin oxide FET gate. In the presence of high voltage or laser power the thin oxide is electrically broken down to change from a non-conducting to a conducting condition. The change in conduction is done without affecting any remaining components of a circuit.
For sensing the logic state of the antifuse device, a sense amplifier is provided to identify the antifuse device to be either non-conducting or conducting. However, the sense amplifier should require very low power consumption in the application of complex communications integrated circuits. In order to satisfy a requirement for low power, small devices are used in the sense amplifier which are susceptible to damage due to overvoltage. What is needed is a device capable of providing both programming capability of the antifuse and electrical isolation from overvoltage of the accompanying sense amplifier.